An ultra-high pressure mercury lamp used typically as a light source for a projector includes a light-emitting bulb having a light-emitting part and a pair of sealing sections interposing the light-emitting part, a pair of metal foils respectively embedded in the sealing sections, a pair of electrodes each having one end protruding into the light-emitting part and having the other end embedded in the corresponding sealing section and joined to the corresponding metal foil, and a pair of leads respectively connected to the metal foils and configured to supply power to the electrodes. Then, high luminance is achieved by increasing a mercury vapor pressure inside the light-emitting part when discharging.
Here, various countermeasures have been proposed in order to prevent failures due to insufficient strength at sealing sections, especially in the vicinity of sections where the electrodes and the metal foils are joined.
Patent Document 1 discloses a technique for reducing a load on a sealing section and preventing a breakage thereof in a way that a stress in the vicinity of an electrode is adjusted by selecting the material of the electrode or by winding a coil to the electrode.
Patent Document 2 discloses a technique for decreasing a difference in thermal expansion between an electrode and quartz glass at a sealing section by wrapping a metal foil around the electrode, and thereby preventing a failure of the sealing section attributed to the difference in thermal expansion.